This invention relates generally to leak resistant vessels and more particularly to vessels which permit, in a controlled manner, passage of liquid out of the vessel upon demand.
Vessels of the type to which the present invention relates are most commonly in the form of drinking cups used for small children. The cups are configured so that if they are turned over, liquid inside the cup is prevented from spilling out of the cup by a valve arrangement that seals the cup when not used. Usually the cup has a relatively rigid cover formed with a spout that the child puts his lips on to drink from the cup. The cover can be releasably attached (e.g., snapped or screwed on) to a container portion of the cup over an open top of the container portion, to close the open top. The valve is arranged between the cover and the container portion can be opened to allow liquid to pass out of the cup for drinking. Most commonly, the valve is actuated by a vacuum pressure applied by the user to the interior of the cup by sucking on a spout or other opening in a cover of the cup. The vacuum pressure so applied causes the valve to move or deform in such a way that a path past the valve is exposed so liquid can flow out of the cup. It is possible that the valve might be actuated in other ways, such as a purely mechanical actuation, but for small children vacuum pressure actuation is most preferable because the only time the valve is open is when the child in the act of taking a drink.
Vacuum pressure actuated drinking cups of the type just described have certain problems generally associated with balancing the need to assure positive sealing with the need to make the cup easy to use for the child. A strong seal by the valve requires a relatively large vacuum to open, making it hard for the child to use. A seal that requires a lower vacuum pressure to open may not seal tightly enough to prevent at least some liquid flowing past it. Frequently, the valve is relatively small and located under the spout. The small size of the valve requires a substantial vacuum pressure to actuate because the pressure acts on only a relatively small area. In other words, children will have to suck with significant effort to get the valve to open. That makes the cup less desirable to the child. It is also important to reduce the opportunity for the child to suck in air when drinking from the cup. This may occur when the level of liquid in the cup is low. If the opening covered by the valve is relatively small, the problem is minimized. However if the valve is also small in surface area, this can lead to difficulty in opening the valve, as previously described.
Conventionally, the valve may be permanently attached to the cover so that the valve will always remain in tact. However, in use the valve will necessarily become fouled with drink liquid and particulates in the liquid. Although cleaning is possible, it is very difficult to clean the entire valve or the entire cover. Disassembly of the valve from the cover would result in destruction of the valve (or cover). Therefore, it is difficult to make certain that the valve and cover remain clean in repeated use. It is known to provide valves that can be disassembled from the cover for cleaning. However, these valves may be difficult to detach and reassemble. Moreover, small valves may become lost or damaged.